The present invention relates to an industrial robot system in which a plurality of robots each having one or more axes are controlled by a single control unit, and all the robots may be simultaneously operated in synchronism with working machines additionally provided in the system.
A conventional industrial robot is composed of a single control unit, a single machine body and a teaching controller for generating commands for teaching. In the case where a work is machined or conveyed by using a plurality of robots, of course, a plurality of control units are to be used. Then, the robots must machine or convey the work is synchronism with mutual interlock signals. For such a synchronism according to the mutual interlock signals, there has been a method for starting the operation after it has been detected that the associated robot is located at a predetermined position and it is confirmed that the subject robot does not interfere with the associated robot even if the subject robot is operated.
According to this method, the robot is operated always after the confirmation that the associated robot is stopped at the predetermined position or is not located in the operational area where the subject robot is to be moved. For this reason, it is necessary to take a waste waiting period of time longer than necessary for the operation itself.
Also, when the work is transferred to the other associated robot or is received from the associated robot, it is impossible to control the relative moving speed of hands of these robots down to zero. It is therefore necessary to give and take the work under the condition that the respective robots are held in a stationary manner. For this reason, the acceleration and deceleration of the robot bodies are carried out more frequently than necessary, which would shorten a mechanical service life of the robots and would lead to waste consumption of energy.
This is also in the case when the working machine is present within the robotic system and the robots feed the work to the working machine or pick up the work thereform. It is impossible for the robot to feed or pick up the work after the confirmation that the working machine has been located at the predetermined waiting position.
Thus, the conventional system composed of the plurality of robots and working machine suffers from the disadvantage that the acceleration and deceleration are repeated with the consumption of energy, and the cycle time is longer than necessary. Therefore, it is impossible to operate the system with a high efficiency.
Also, a conventional robotic program is composed of elements such steps for representing the reproduction order of the program, step data for representing the physical position of the steps, a time period for the movement between the steps, and some input/output signal processing for each step.
The movement period between the steps represents a designated time period for the movement between two positions, which time period has a difference from the actual movement time. Although the total of the designated time periods of the respective steps should be the cycle time, each step has an error and the error is accumulated to generate a large error for the cycle time as a whole. Furthermore, in the conventional positional control method, commanded positional data are designated for a subsequent step after the confirmation that the robot has reached the commanded position. For this reason, the waiting time is added to the cycle time for every step, and it is impossible to determine the cycle time unless the system is actually operation.
Even if the plurality of robots are controlled by a single control unit, it is impossible to make the cycle times of all the robots at the same one in accordance with the foregoing positional control method. Accordingly, although signal wires are not actually connected to each other, the synchronizing method for the robots within the system is equivalent to the mutual interlock method.